1. Field of the Invention
The present invention relates to an improved continuous flow chemical reaction apparatus wherein the introduction of at least one reactant feed into the reaction zone is optimized. The invention also relates to improved chemical reactions achieved using the continuous flow chemical reaction apparatus.
2. Description of Related Art
Several publications are referenced in this application. The references describe the state of the art to which this invention pertains, and are hereby incorporated by reference.
An oxidative dehydrogenation, or partial oxidation, process is a one step conversion of light hydrocarbons to olefins and carboxylic acids. The process potentially offers many advantages over cracking and pure dehydrogenation which are extremely capital intensive and energy intensive. The conversion of saturated hydrocarbons into olefins and carboxylic acids over low temperature catalysts was disclosed by Thorstienson et al. in a report published in Journal of Catalysis, vol. 52, pp. 116–132 (1978).
U.S. Pat. No. 4,250,346 discloses a process for oxidative dehydrogenation of ethane to ethylene suggesting different low temperature catalyst systems. European Patent No. EP 0 518 548 A2 discloses a process for making acetic acid which comprises oxidizing ethane with molecular oxygen in a reaction zone at a pressure at least 100 psig while the reactants are in contact with a solid catalyst containing vanadium and phosphorous oxides (VPO system).
The oxidative dehydrogenation reaction, however, raises problems such as: (a) removal of the exothermic heat of reaction, (b) possible associated temperature runaway, (c) control of selectivity to desired product, and (d) limiting the formation of undesired oxygenated by-products and carbon oxides.
Another problem which is associated with oxydehydrogenation processes, as well as oxidation processes, is the limitation on the oxidant to hydrocarbon feed ratios which is imposed by the explosive mixture formation constraint. This problem compromises the ability of the process to achieve optimality of feed compositions that satisfy the stoichiometric and kinetic requirements of the reaction, yet avoid compositions which can lead to autoignition, deflagration, and detonation.
These problems have been addressed in a number of patents. Each tried to overcome one or more of the difficulties mentioned above by proposing a modified reactor system or different reactor arrangement.
U.S. Pat. No. 4,899,003 issued to Union Carbide relates to multi-staging the reactor system where a feed gas comprising ethane and oxygen is converted over an oxydehydrogenation catalyst to a product gas comprising ethylene, acetic acid, water, ethane, and carbon oxides. The product gas from each stage (other than the last stage) is cooled and a portion of the acetic acid and water is separated and oxygen is added before passing the product gas stream to the next reaction stage. Total oxygen content in the feed stream to any of the reactors was maintained below 6 mole percent with respect to the total input gaseous stream in that stage.
U.S. Pat. No. 5,583,240 issued to SRI relates to a reactor with porous membranes to provide for the continuous addition of one reactant all along the reactor and mixing in the entire volume of the reactor to minimize or eliminate local high concentration gradients and hot spots. The other reactant is flowed through the inside of the permeation tube, which contains mixing elements. Those mixing elements were claimed to increase the yield of desired product by increasing the heat and mass transfer rates.
European Patent No. EP 546 677 A1 relates to a fluidized bed for ethane oxidation to acetic acid. The disclosed process included three key steps: (1) cooling the gaseous effluent from the reaction zone; (2) separating most of the acetic acid in liquid form from the effluent gases, leaving a gaseous stream containing nearly all of the carbon oxide contained in the effluent; (3) purging a small portion of said gaseous stream and recycling most of the gaseous stream as part of the feed to the reaction zone. Purging is intended to prevent build-up of carbon oxides in the reaction zone, while recycling serves to maintain a high proportion of carbon oxides in the reaction zone gases, thus aiding in moderating the temperature elevating effect of the highly exothermic oxidation reaction.
U.S. Pat. No. 5,723,094 relates to a chemical reactor design which provides improved micro-mixing conditions and reduced localized zones of concentration to increase reaction selectivity to desired products. The design includes a capillary tubelet positioned within and along the length of flow tubes positioned in a shell reactor and one or more distributors for distributing a first reactant into the flow tubes and a second reactant into the capillary tubes.
European Patent Publication No. 0 532 325 relates to a method and apparatus for the production of ethylene oxide. European Patent Publication No. 0 383 224 relates to a shell-and-tube reactor and method of using the same.
It would be desirable to provide a continuous flow chemical reaction system which provides optimality of feed compositions along a substantial portion of the reaction zone and satisfies the stoichiometric and kinetics requirements of the reaction while maintaining the reaction mixture within the explosive mixture formation constraint and thus avoid reactant mixtures which can lead to autoignition, deflagration, and detonation.